Detection of potentially toxic metals by SERS using salen complexes

Surfaced enhanced Raman scattering (SERS) can discriminate between metal complexes due to the characteristic "spectral fingerprints" obtained. As a result, SERS has the potential to develop relatively simple and sensitive methods of detecting and quantifying a range of metal ions in solution. This could be beneficial for the environmental monitoring of potentially toxic metals (PTMs). Here, salen was used as a ligand to form complexes of Ni(ii), Cu(ii), Mn(ii) and Co(ii) in solution. The SERS spectra showed characteristic spectral differences specific to each metal complex, thus allowing the identification of each of these metal ions. This method allows a number of metal ions to be detected using the same ligand and an identical preparation procedure. The limit of detection (LOD) was determined for each metal ion, and it was found that Ni(ii), Cu(ii) and Mn(ii) could be detected below the WHO's recommended limits in drinking water at 1, 2 and 2 μg L^-1, respectively. Co(ii) was found to have an LOD of 20 μg L^-1, however no limit has been set for this ion by the WHO as the concentration of Co(ii) in drinking water is generally <1-2 μg L^-1. A contaminated water sample was also analysed where Mn(ii) was detected at a level of 800 μg L^-1.